This study mainly explored the associations between preoperative CONUT score and tumor prognosis among colorectal cancer patients. The pre-operative CONUT ≥ 5 was independently correlated with a 3.92-fold of increased risk of poor OS and a 2.99-fold increased risk of poor RFS. By comparison, we found that the predictive power of the CONUT score was more accurate than that of other nutritional indexes. In addition, we also found that the CONUT score was in paralleled with the body skeletal muscle index, which strongly represented body protein reserve and nutritional state. Therefore, the CONUT score may serve as an optimal prognostic nutritional index to predict the long-term outcome after radical surgery for colorectal cancer.
In recent years, there are many researches on nutritional status and tumor prognosis. The level of skeletal muscle mass was currently considered as the optimal indicator of nutritional status of patients. Jingjie Xiao 9 et al. found that preoperative skeletal muscle level could predict tumor prognosis. As reported, those with a pre-operative diagnosis of sarcopenia had a 1.1-1.2-fold higher incidence of postoperative complications, 2-fold increased risk of death within 30 days after surgery than those without sarcopenia among colorectal cancer patients 6–9. Nonetheless, skeletal muscle measurement method is not widely promoted because of its consumables, time consuming, power consuming, insecurity and other disadvantages. Therefore, to identify a relatively convenient and safe early prediction indicator was warranted. Although Allan M. Golder21 and Nozoe T22 et al. found that mGPS, NLR and PNI indexes could serve as prediction tools for prognosis in multiple cancers, the predictive power of such indicators remained unsatisfactory. In our study, the accuracy of the CONU score was higher than that of mGPS, NLR and PNI. Consequently, the CONUT score showed satisfactory prediction performance. This objective, safe, simple and easy, accessible tool was more conducive to early and rapid prediction and has clinical application value.
As a nutritional status score, the effective role of the CONUT score has been clinically proven to evaluate nutrition14. The predictive ability of CONUT to predict the prognosis of colon cancer may be related to its three components. Firstly, the serum albumin was a biomarker for systemic inflammation. Tumor prognosis was highly correlated with inflammation state. Excessive inflammatory activation affected the tumor microenvironment 23 and suppressed normal immune reactions 24. Secondly, Zhang YY25, Zhao J26, et al. demonstrated that colon cancer patients with reduced lymphocyte counts had worse prognosis than patients with normal lymphocyte counts. Lymphocytes, as immune cells of the human body, could recognize and kill tumor cells through humoral and cellular immunity pathways, thus playing a significant role in inhibiting tumor cell proliferation and metastasis27. Thirdly, cholesterol is mainly synthesized in the liver and exists in blood in the form of low-density lipoprotein (LDL). LDL receptor (LDLR) was expressed on the surface of normal cells and tumor cells. Through the binding of LDLR to LDL, the LDL in serum enters cells through endocytosis28. Different from normal tissues, LDLR could not limit intracellular cholesterol transportation through feedback regulation 29. Therefore, it was unrestricted for tumor cells to transport cholesterol into cells to provide energy. Moreover, cancer cells could also use the metabolites produced by cholesterol metabolism to synthesize substances that can promote their growth and development 30,31. Therefore, low serum cholesterol level could be the result of an increased risk of cancer, indicating a poor prognosis. In conclusion, The ability of the CONUT score to predict prognosis may be due to its comprehensive reflection of the body's nutritional status, inflammatory status, immune status and tumor metabolism.
Besides, our study also found a correlation between CONUT score and skeletal muscle level. (R2 = 0.137, correlation coefficient − 0.319, p<0.01), possibly because both scores reflect the protein reserve of the body. Patients with cancer, especially those who underwent surgery procedures, could experience larger demand for energy and protein intake than normal people 32. Inadequate energy or protein intake would accelerate the glycogenolysis process leading to glycogen depletion, further promoting gluconeogenesis and leading to body skeletal protein decomposition33. Patients would be unable to tolerate surgery, delay recovery, and even more prone to tumor recurrence, resulting in a poor prognosis when protein reserver was insufficient. This may also be one of the factors contributing to the predictive power of CONUT scores.
The present study had several limitations. First, this study was a retrospective single-center study comprised of patients from the same region, which was homogeneous in a race. Second, the sample size was small and the follow-up time was not long enough. Last, the post-operative CONUT was not followed up and the nutritional status of patients could not be assessed dynamically. Therefore, prospective studies are warranted further to confirm the predictive significance of the CONUT score.